1. Field of the Invention
The present invention relates to a torque converter comprising an impeller member a turbine member and a stator member, as well as a fluid flow path formed through these three members which has a cross-section formed into an elliptical or flat configuration in which the axial width is less than the diametrical length.
2. Description of the Related Art
In the construction of a torque converter, a flow path is formed through an impeller member, a turbine member and a stator member for circulation of oil. The impeller member is driven to rotate by the engine so as to generate a flow of oil by vanes of the impeller member, so that the oil flow so generated strikes against the turbine vanes to thereby rotate the turbine member. Then, the oil flow emerging from the turbine flows into the impeller member while deflecting the oil flow by vanes of the stator member, whereby the rotational driving force is transmitted from the impeller member to the turbine member. An internal fluid flow path formed generally into a toroidal shape having a circular cross-section has been known as used for the internal flow path of a torque converter as described above. Additionally, a toroidal flow path is also known which has a flattened circular or elliptic cross-section. Thus, hereinafter, a torque converter having a flow path of a circular cross-section is referred to as a circular cross-section torque converter, whereas a torque converter having a flow path of a flat cross-section as a flat cross-section torque converter.
While the flat cross-section converter is advantageous in that the axial dimension can be reduced, it has a shortcoming in that fluid tends not to flow smoothly inside due to its flat flow path, therefore leading to a risk that the performance of the torque converter is deteriorated. To counteract this, conventionally there have been proposals to provide torque converters which are formed as flat as possible without deteriorating the performance of the torque converter, such as torque absorbing capacity and transfer efficiency, some of which are disclosed in, for instance, JP-B-57-37791and JP-A-4-254043.
Here, having a flat torque converter is advantageous not only in reducing the torque converter""s axial dimension but also in reducing the weight and production cost thereof. Moreover, reducing the axial dimension of a torque converter facilitates the realization of a multi-step transmission which connects to the torque converter, thereby making it possible to have a better fuel economy as well. To this end, there have conventionally been proposed various types of flat cross-section torque converters, but with those proposals, configurations of torque converters were individually specified under certain conditions, and therefore design methods have been desired which can be applied generally and universally.
The present invention was made in view of these situations, and an object thereof is to provide an optimal design method for an internal flow path for a flat cross-section torque converter. A further object of the present invention is to provide a flat cross-section torque converter in which the torque converter can be flattened without deteriorating the performance thereof such as torque absorbing capacity and transmission efficiency.
With a view to attaining the above objects, according to the present invention, there is provided a torque converter wherein in an axial cross-section of a fluid flow path formed through an impeller member (for instance, an impeller 11 as described in an embodiment of the invention), a turbine member (for instance, a turbine 12 as described in the embodiment) and a stator member (for instance, a stator 13 as described in the embodiment) which constitute the torque converter, a flatness (2L/H) and a torus inside and outside radius ratio (r/R) which are defined based on a distance 2L between axial ends of the flow path, a maximum radius R, a minimum radius r and a difference H (=Rxe2x88x92r) between the maximum radius R and the minimum radius r satisfy equation (1) and equation (2). Moreover, in the axial cross-section, assuming that an axially central position (for instance, point 0 as shown in FIG. 2) of the flow path along a rotational shaft of the torque converter is an origin, an axial direction an X direction and a radial direction a Y direction, the configuration of the flow path is set such that the position of a point of contact (for instance, a point of contact as shown in FIG. 2) between a straight line (for instance, a straight line C as shown in FIG. 2) inclined 45degrees relative to the X direction and a curve (for instance, a curve D as shown in FIG. 2) constituting an external circumference surface of the flow path in the turbine member is located within an area (for instance, a hatched area F as shown in FIG. 2) surrounded by a first straight line (for instance, a first straight line A as shown in FIG. 2) which is expressed by equation (3) and a second straight line (for instance, a second straight line B as shown in FIG. 2) represented by equation (4).
0.55 less than (2L/H) less than 0.75xe2x80x83xe2x80x83(1)
0.35 less than (r/R) less than 0.40xe2x80x83xe2x80x83(2)
Y=(R/L)xc3x97X+(6/4)xc3x97Rxe2x80x83xe2x80x83(3)
Y=(R/L)xc3x97X+(7/4)xc3x97Rxe2x80x83xe2x80x83(4)
According to results of various calculations and experiments carried out by the inventor of the present invention, in a flat cross-section torque converter which satisfies the equations (1) and (2), not only can the radius of curvature of the curve defining the flow path inside the turbine be reduced but also an internal flow path can be formed which can allow the oil flow therein to deflect smoothly provided that the configuration of the flow path in the turbine member is set such that the position of the point of contact between the straight line inclined 45degrees relative to the X direction and the curve constituting the external circumference surface of the flow path in the turbine member is located within the area surrounded by the first straight line which is expressed by the equation (3) and the second straight line expressed by the equation (4). This can help not only reduce a fluid loss (generation of eddy currents or the like) at an entrance portion to the turbine where a large fluid loss tends to be found but also improve the torque absorbing capacity and transfer efficiency of the torque converter. As a result of this, a torque converter can be obtained which has a flat cross-section and a small axial dimension, and provides a better torque converter performance.